1. Field of the Invention
This invention relates in general to the field of material handling equipment. In particular, the invention relates to torque wrenches for making and breaking connections between sections of drill pipe.
2. Description of the Prior Art
U.S. Pat. No. 4,348,920 (Boyadjieff), issued Sept. 14, 1982, shows a power driven tool for making and breaking threaded connections between drill pipe sections. The tool includes a movable carriage, a well pipe spinner, and two torque wrench assemblies. The torque wrench assemblies are used to make and break connections between the tool joints on upper and lower pipe sections. The spinner is used to rotate the upper pipe section rapidly into or out of connection with the lower pipe section.
Each torque wrench assembly has a gate, a latch, and a clamp, for clamping onto the tool joint on the end of the section of drill pipe. Each torque wrench assembly is rotatable relative to the other wrench assembly, and has torque cylinders to apply torque in either direction to the tool joint. The clamps and the torque cylinders are hydraulically powered.
Larger diameter drill pipe generally requires a higher torque pressure to make and break connections. Sufficient clamping pressure must be maintained, or the pipe will slip as increased torque is applied to the connection. However, excessive clamping pressure can damage the pipe.
It has been known, therefore, to provide for variable torque pressure and clamping pressure. These pressures are varied by manually adjusting a pair of hydraulic valves in the hydraulic system of the tool. If either pressure was increased too quickly, either the pipe was damaged by excessive clamping pressure, or the pipe slipped because of insufficient clamping pressure.